Printing with an ink-jet recording system involves discharging ink from a nozzle, and bonding that ink to a recording target material, and because the nozzle does not contact the recording target material, favorable printing can be achieved even onto curved surfaces or uneven surfaces with irregular surface forms. As a result, there is a wide range of industrial fields to which ink-jet printing can be applied.
Amongst the different inks used in ink-jet recording systems, those which use a dye as the coloring material can be broadly classified into water-based inks, which use water as the primary solvent, and oil-based inks, which use an organic solvent as the primary solvent, although water-based inks, in which a dye is dissolved in a water-based medium, are more common. However, when conventional water-based dye inks are used in industrial applications, a variety of problems arise, including a slow drying rate for ink applied to non-absorbent materials, weak adhesion of the printed image, and unsatisfactory durability in terms of factors such as the abrasion resistance, the water resistance and the light resistance. One example of inks that are able to largely overcome these problems are the water-based and oil-based ultraviolet curable ink-jet recording inks, which use various pigments as the coloring materials, and undergo curing and drying through exposure to an activated energy ray such as ultraviolet light.
Examples of oil-based ink-jet recording inks that undergo curing and drying through exposure to an activated energy ray such as ultraviolet light include the inks disclosed in the examples of Published Japanese Translation No. 2001-525479 of PCT, which contain carbon black, a dispersant, and a dispersion assistant, wherein the dispersion assistant uses an amine salt of copper phthalocyanine sulfonic acid, and the inks disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-207098, which use a copper phthalocyanine derivative with an introduced functional group such as a phthalimidomethyl group, amino group or triazine group as a pigment dispersant.
However, all of the inks disclosed in Published Japanese Translation No. 2001-525479 of PCT and Japanese Unexamined Patent Application, First Publication No. 2001-207098 use a lipophilic phthalocyanine derivative that can be easily dispersed in the photopolymerizable compound, and consequently the adsorption of the phthalocyanine derivative of the dispersion assistant to the carbon black is prone to desorption, meaning the dispersion stability of the pigment within the photopolymerizable compound is unsatisfactory.
If the dispersion stability is unsatisfactory, then aggregates are more likely to form in the ink, and the adhesion of these types of aggregates around the vicinity of the ink-jet nozzle can prevent the formation of favorable ink droplets at the nozzle, leading to a marked deterioration in the stability of the discharge volume and discharge direction.
Currently, the dispersion stability of ultraviolet curable ink-jet recording inks that use carbon black as the coloring material is not entirely satisfactory, meaning the discharge stability of these inks is also unsatisfactory. Achieving a favorable dispersion stability is particularly difficult in high resolution inks that use carbon black with a small particle size.